you can buy a stop cock,with compression fittings,which comprises of the valve,fixing nuts for both ends and compression olives,at a cost of around £3 to £5. Cut out the piece of pipe,in such a way that the new fitting will fit in the gap,push the nuts on to each side of the pipe,followed by the olives,then you are readt to join the nuts to the fitting,tighten up,but not excessively,with 2 spanners,1 on each nut,try to tighten each nut evenly,job done,easy...if you cant isolate the supply before starting the job,then you should buy a pipe freezing kit,around £20,these usually give you 30 minutes to do the job.
mark, December 2008